1. The Field of the Invention
The present invention relates to an endoprosthesis for delivery and deployment within a body vessel of a human or animal. More particularly, the invention relates to an endoprosthesis with improved strain distribution.
2. The Relevant Technology
Stents, grafts, and a variety of other endoprostheses are well known and used in interventional procedures, such as for treating aneurysms, for lining or repairing vessel walls, for filtering or controlling fluid flow, and for expanding or scaffolding occluded or collapsed vessels. Such endoprostheses can be delivered and used in virtually any accessible body lumen of a human or animal, and can be deployed by any of a variety of recognized means. One recognized use of endoprostheses, such as stents, is for the treatment of atherosclerotic stenosis in blood vessels. For example, after a patient undergoes a percutaneous transluminal coronary angioplasty or similar interventional procedure, a stent is often deployed at the treatment site to improve the results of the medical procedure and to reduce the likelihood of restenosis. The stent is configured to scaffold or support the treated blood vessel. If desired, a stent can also be loaded with a beneficial agent so as to act as a delivery platform to reduce restenosis or for other beneficial purposes.
An endoprosthesis is typically delivered by a catheter delivery system to a desired location or deployment site inside a body lumen of a vessel or other tubular organ. To facilitate such delivery, the endoprosthesis can be capable of having a particularly small cross-sectional profile to access deployment sites within small diameter vessels. Additionally, the intended deployment site may be difficult to access by a physician and can involve traversing the delivery system through a tortuous luminal pathway. Thus, it can be desirable to provide the endoprosthesis with a sufficient degree of flexibility during delivery to allow advancement through the anatomy to the deployed site. Moreover, it can be desirable for the endoprosthesis to have sufficient strain distribution or crack and/or fatigue resistance so as to retain structural integrity during and/or after being deployed and set.
Generally, an endoprosthesis can be constructed of multiple annular members or rings that are interconnected either through a connection section or a connection element. Accordingly, flexibility of the endoprosthesis can be controlled by the number and/or width of the rings, the characteristics of connection sections or elements, and/or the thickness of material that forms the rings and/or connection elements. Although it is not specifically known how much vessel restenosis can be attributed to stent rigidity, it is know that a reasonably stiff stent may injure the vessel during motion (e.g., vessel contraction and/or expansion during pulsatile blood flow). As such, it can be desirable for an endoprosthesis to have sufficient flexibility/stiffness properties to enable deployment through a tortuous luminal pathway. Also, it can be desirable to change the stiffness properties of the endoprosthesis after deployment within a vessel. However, it can also be important for the endoprosthesis to retain its structural integrity after deployment by being configured to inhibit the formation and/or propagation of cracks as well as resist structural fatigue.
Once deployed, the endoprosthesis can be capable of satisfying a variety of performance characteristics. The endoprosthesis can be sufficiently rigid or provide an outwardly-oriented bias when deployed to perform its intended function, such as opening a lumen or supporting a vessel wall. Similarly, the endoprosthesis can have suitable flexibility along its length and/or width to inhibit any kinking or straightening that may occur during deployment or setting within the tortuous luminal pathway.
A significant failure mode in endoprostheses can be a result of significant and/or localized strains that the endoprostheses experience during crimping, deployment, and/or setting. These significant and/or localized strains can result in elastic spring-back or recoil during crimping and/or expansion of the endoprostheses. These strains can also lead to distortion, structural fatigue, and/or crack formation in the endoprostheses. For example, failure can result from a stent element, such as an elbow, beginning to crack during crimping, setting, and/or use. Such cracks can also form and/or propagate through the material of the endoprosthesis as a result of the cyclic loading that the stent undergoes during the pulsatile movement of blood and associated vessel expansion and contraction.
Although various endoprostheses have been developed to address one or more of the aforementioned performance shortcomings, there remains a need for a more versatile design that improves one or more performance characteristics without sacrificing the remaining characteristics. Therefore, it would be advantageous to have an endoprosthesis configured to have increased and/or enhanced strain distribution to resist cracking or fatiguing during crimping, deployment, setting, and/or use. Additionally, it would be beneficial for the endoprosthesis to have sufficient strength and flexibility to enable deployment through tortuous luminal pathways while retaining the ability to perform its intended function.